1. Field of the Invention
The present invention relates to an automatic focusing control technique of a camera, and more particularly to a method for controlling focusing areas of a camera for partitioning a picture picked up by an optical system into a plurality of areas, and an apparatus for executing the same.
2. Description of the Prior Art
A technique for controlling auto focusing of a camera is used for detecting a subject by using a luminance signal of the subject that is picked up via a camera lens, and driving an optical system to be fitted to the detected subject, thereby automatically adjusting its focus. FIG. 1 illustrates a block diagram showing a conventional circuit for controlling auto focusing of a camera.
Referring to FIG. 1, the conventional circuit for controlling the auto focusing of the camera includes an optical system 10 including an objective lens 10a, a zoom lens 10b, an iris 10c and a focusing lens 10d, and a charge-coupled device (hereinafter simply referred to as "CCD") 20 for converting an image of a subject picked up via optical system 10 into an electric signal. Additionally, an automatic gain controller (hereinafter simply referred to as "AGC") circuit 30 carries out automatic gain control of a video signal converted by means of CCD 20. A digital signal processing section 40 digitizes the AGC-processed video signal, and separates it into a luminance signal and a chrominance signal to process the obtained signals, and a high-pass filter 42 filters an output luminance signal of digital signal processing section 40 to provide only high band components thereof. An area setting section 44 sets an area for performing focusing controlling by using the high-pass filtered luminance signal as an input, and an evaluation value detecting section 46 detects an evaluation value of the subject luminance signal within the area which is set in area setting section 44. In addition to these, a controlling section 48 judges whether the subject is detected or not by means of the evaluation value detected in evaluation value detecting section 46 and provides a focusing area control signal and a lens driving control signal in accordance with the result of the determination. A motor driving section 130 receives the lens driving control signal from controlling section 48 and provides a driving signal. A focusing lens motor 140 drives focusing lens 10d in accordance with the driving signal.
The image picked up by optical system 10 is converted into an electric video signal in CCD 20 via objective lens 10a, zoom lens 10b, iris 10c and focusing lens 10d. Then, the resultant video signal is automatically gain-controlled by AGC circuit 30 to be supplied into digital signal processing section 40.
An A/D converter 40a of digital signal processing section 40 converts an analog video signal input into a digital signal, and an Y/C separator 40b separates the digital video signal into luminance signal Y and chrominance signal C.
Separated chrominance signal C is processed via a chrominance signal processor 40c, and luminance signal Y is processed via a luminance signal processor 40d. By doing so, a composite video signal CVS is obtained by adding signals C and Y in adder 40e.
At this time, the luminance signal provided from luminance signal processor 40d is filtered by high-pass filter 42 to provide only the high band components of the luminance signal corresponding to the outline portion of the image, and area setting section 44 receives the high-pass filtered luminance signal to execute the auto focusing controlling upon the subject picked up by optical system 10.
More specifically, in the conventional technique as shown in FIG. 2, a picture area is set by a first area A1 and a second area A2, in which the auto focusing operation is performed depending on whether the subject is detected within first area A1 or not after first area A1 is fixed.
In this case, the picture area is divided into two areas A1 and A2. Unless subject is detected within area A1, the subject is detected in its expanding area A2 to continuously maintain its expanding area A2.
In association with the foregoing detection of the subject and auto focusing operation, a luminance signal level of the subject detected in the corresponding area is detected by evaluation value detecting section 46. Thus, in accordance with the result of comparing the detected value with a predetermined reference value, the auto focusing is performed by driving lens driving motor 140 via motor driving section 130.
That is, the subject picked up by optical system 10 involves a distinct difference (or change) in the luminance signals between the subject and the background image. Due to this fact, by evaluating the luminance signal value, the presence or absence of the subject corresponding to the background image can be detected. Thereafter, the auto focusing is accomplished by driving the lens to the direction and position where the luminance signal having the maximum level is detected, to be matched with the detected subject.
In the above-described conventional technique for dividing the picture area into areas A1 and A2 and variably controlling the areas as shown in FIG. 2, the auto focusing is performed by detecting the subject under the state of changing into area A2 unless the subject is detected in area A1. However, area A2 is continuously maintained even after executing the auto focusing to have a drawback that, if a new subject is joined later, the auto focusing upon multiple subjects caused by the new subject becomes impossible in expanding area A2.